The administration of hormones to control the reproductive process in domestic animals such as horse, cows, sheep, goats and swine is well known in the art. One approach to managing reproductive processes in domestic mammals involves the direct administration of gonadotropins to domestic animals. Gonadotropins are produced by the anterior lobe of the pituitary gland and are characterized as follicle stimulating hormone (FSH) and luteinizing hormone (LH). Typically such hormones are extracted from the porcine pituitary glands and are administered to domestic animals to control or stimulate the ovulatory process. One gonadotropin formulation is FSH-P produced by Schering-Plough Corp. FSH-P has a fairly high and variable content of luteinizing hormone and while effective in producing an ovulatory response, has been less than desirable in producing high fertilization rates and viable embryos. Another formulation, which contains a low and controlled level of luteinizing hormone with high follicle stimulating activity, is disclosed in U.S. Pat. No. 4,780,451 to Donaldson. Gonadotropin release hormone (GnRH) can also be used to stimulate ovulation as related in U.S. Pat. No. 5,180,711 to Hodgen. In that instance GnRH is administered subsequent to a GnRH antagonist which effectively suppressed natural gonadotropin levels. The GnRH then stimulates the release of endogenous FSH and LH leading to follicle development and ovulation. The use of similar hormones for control of ovulation in cattle is described in U.S. Pat. No. 5,589,457 to Wiltbank.
A number of different preparations of gonadotropins are available commercially including Fertagyl, Cystorelin, Chorulon, Folltropin-V, Factrel, PG600, Receptal and others. In addition, certain GnRH analogs, or agonists, such as deslorelin and buserelin are also available. These hormones may be administered to the various domestic species by implant, by intramuscular or subcutaneous injection or by mucosal applications such as intranasal and intravaginal routes. Gonadotropins may also be administered with excipients or delivery systems, which delay or control the release over time to produce more natural or even extended release patterns of LH. See U.S. Pat. No. 6,051,558 to Burns, et. al.
A major goal of commercial swine production is to maximize reproductive efficiency. Increased reproductive efficiency offers producers substantial opportunities to reduce production costs and enhance profitability. Part of the production costs is the result of a heavy reliance on daily heat detection of individual animals (W. L. Flowers and H.-D. Alhusen, (1992) J. Animal Science 70:615-621) since gilts and sows are bred based on spontaneous estrus cycles. Approximately half of the labor in swine breeding facilities is devoted to detection of estrus in breeding gilts and sows. Gilts or sows must be checked at least once daily in order to be bred at the correct time, and, if artificial insemination (“AI”) is used, it may be necessary to check twice daily in order to achieve the best results. Rigorous heat detection is necessary because it is difficult to predict the day of heat for any cyclic gilt or open sow, even with good heat detection records.
It is therefore an object of the present invention to provide a means of inducing ovulation that allows thr artificial insemination in the absence of heat detection.